Screen resolution of a mobile device, such as a mobile phone, a PMP and a PDA, has been gradually improved, and mobile devices such as i-Phone and tablet PC can also recently provide high quality video services. A home TV with screen resolution of 1920×1080 or more, that is, a level of full-HD, has been generalized together with the release of a digital TV, and thus a frame rate has been increased. An ultra HDTV (UHDTV) having resolution of 4K or 8K (for example, 7680×4320) based on a horizontal direction of the screen has attracted attention as a next-generation TV.
Image compression technologies capable of improving efficiency of image compression together with improvement of resolution of a display device have been developed and used. An amount of calculation for compression and restoration of an image increases as an image size increases and a frame rate increases.
As a method for reducing power consumption while processing a large amount of calculation, a multicore processor in which multiple CPUs exist in one chip was developed and has been universally used for a PC, a notebook computer and the like, and has been rapidly applied to a smart phone and a tablet PC.
In a general image compression scheme in the related art, in order to effectively compress image data, an original image is divided into several blocks having a predetermined size to be processed, and one block includes adjacent pixels on the image. For example, in a case of the H.264/AVC standard, an image is divided and processed by a macroblock unit, and the macroblock includes one luminance sample block having a size of 16×16 and two chrominance sample blocks (a size of the chrominance sample block may vary according to a format of an input image). FIG. 1 is a diagram illustrating a method of dividing an image into macroblocks having a size of 16×16 according to the related art. As such, an entire image is divided into the macroblocks having a regular size, so that an encoding process or a decoding process is performed by the macroblock unit.
In order to prevent a decoded image from being deteriorated due to errors of a transmission line, the image compression standard in the related art uses a method of encoding an original image by dividing the original image into multiple slices, and thus an error generated in one slice is not propagated to another slice. For example, as illustrated in FIG. 2A, the MPEG-4 standard uses a method of constituting a slice by grouping multiple macroblocks in the order of a raster scan. In the H.264/AVC standard, a slice is constituted in various methods, such as a method of constituting a slice in an arbitrary order regardless of a scanning order as illustrated in FIG. 2B, a method of alternately allocating continuous macroblocks to different slice groups as illustrated in FIG. 2C, and a method of allocating macroblocks included in a predetermined quadrangular area to different slice groups as illustrated in FIG. 2D.
In the meantime, the aforementioned method of dividing the image into the slices or the slice groups may be used for the purpose of dividing and performing an image encoding or decoding process through multiple processors, as well as for reducing an influence of errors in transmission and decoding of the image. FIG. 3 is a diagram illustrating a method of dividing one image into multiple slices, simultaneously encoding the divided slices by multiple image encoding processors, and then combining the encoded images into one bit stream.
However, in a case of using the method in the related art, it is impossible to use compression information on an adjacent slice, so that compression efficiency is deteriorated compared to a case of encoding an entire image into a single slice, and an image quality is unavoidably deteriorated in continuous predetermined areas of a decoded image when an error is generated in a transmission line. When the continuous macroblocks are allocated to the different slice groups in the method of FIG. 2C or in a similar manner thereto, the deterioration of the image quality due to the error may be dispersed to the entire image, but compression efficiency is further deteriorated.